The prophylactic granulocyte transfusion trial demonstrated a much increased rate of alloimmunization in granulocyte recipients, suggesting that this should not become routine transfusion practice. Autologous frozen platelets continue to be a major part of the transfusion program and platelets from patients with chronic myelogenous leukemia are presently being frozen for use in the blastic phase of the disease. Fourteen successful transfusions of platelets frozen for more than three years have been carried out. Cell collection studies have demonstrated that platelets collected with the Haemonetics Model 30 function and circulate normally. A study has been begun of lymphocyte poor platelets in an effort to demonstrate whether this product can decrease the rate of alloimmunization. It has been demonstrated that one hour after transfusion platelet counts represent a simple and accurate diagnostic tool for the detection of alloimmunization.